Multistage valve



P. KAPTl-:VN 2,015,326

MULT I STAGE VALVE April 13, 1937.

Filed May 4, 1932 Patented Apr. 13, 1937 UNITED STATES MULTIS TAGE VALVE Paul Kapteyn,

Berlin, Germany Application May 4, 1932, Serial No. 609,130

In German 2 Claims.

As well known, it is essential, more particularly in the case of multi-stage high frequency ampliers, to dispose the different lines possessing a high frequency potential so as to be protected against each other, or in such fashion that their mutual capacity is very small.

This requirement is particularly important in connection with hig -frequency multi-stage valves, in which owing to the use of a plurality of systems in a glass bulb and the particularly non-dissipative construction amplifications of particular strength require to be controlled in reliable fashion with construction in a minimum of space. In particular, there occurs in thecase D of two-system valves even with the Yexistence of very small capacities between the anode vof the second system and the control grid of the first system a back-coupling effect, which renders stability of the amplifier a matter of doubt. An additional adverse coupling is caused in the case of inductive loading of the second anode circuit by the grid-anode capacity of the second system.

As extensive tests have shown, diminishment of the iirst-rnentioned coupling (anode of the second system and control grid or the first system) down to a degree which is sufficient even in the case of valves of very high output is only possible if the first system is screened off against the second one. Screening-01T of this nature may be performed, for example, by means of a metal plate (sheet metal or the like) or a close-mesh metal network, whichextends as closely as possible up to the inner wall of the glass bulb and is preferably taken to earth. A screening-off of this nature is provided in the drawing between the systems 2 and 3 and is designated 4.

Further it is necessary to conduct either the anode of the second system or the control grid of the first system out of the glass bulb at a point which is as remote as possible from the remaining lead points. It is also of advantage to coat the glass bulb of the valve in the known manner on the outside with an earthed conductive surface, in order in this manner to reduce all couplings to a minimum. A coating of this nature on the glass bulb is preferably produced in a metal spray process.

The coupling of the anode of the second system and the control grid of the same system may be reduced, in the known manner by the inclusion of a protecting or screening grid between the control grid and the anode.

in addition to the systems the coupling elements, condensers. resistances and chokes., it is dicult However, in the` case of a multi-stage valve, which also includes y May 6, 1931 (ci. 25o-27.5)

as well as the effective anode-cathode capacity of the second system to an undesirable extent, as the former loads the anode alternating potential of the first valve, whilst the latter in the case of'purely a periodic amplification also of the second system reduces the anode alternating potential of the second system.v In addition, a screening-olf of this nature does' not permit of construction on a small space.

According to the invention, the coupling elements are, therefore, provided in that separately v screened portion of the valve which contains the rst system of the multi-stage Valve. In this manner it is possible to make the lead to the grid of the second system so short that the coupling between the anode and the grid lead of the second system remains within the permissible bounds.

In the case of a valve, in which the anode of the second system is passed out at a point remote from the remaining lead points, in which the two amplifier systems are screened off against each other, and in which the coupling systems between the two amplifier systems are arranged on the side of the screen which contains the first system, it is also possible to control in reliable fashion a several-thousand power amplification (approximately 200G- 5000 power) in one single valve. It has been found, however, that in valves of this description the fitting of the coupling elements in the vicinity of the first system causes an undesirable increase in the control grid-anode capacity of the first system. In the case of ohmic anode resistances and the capacitative loading of the first anode circuit, always existent in connection with high frequencies by reason of the connection capacities, there occurs in this manner a reactive eiect on the grid circuit of the first system, which effect makes itself apparent in the form of additional attenuation and a frequency-dependent increase of the effective capacity between the grid and the cathode. Assuming the grid circuit constitutes a resonant circuit, both effects are extremely undesirable for reasons associated with the selection. 'Ihe main share of this detrimental coupling is borne by the capacity between the lead to the control grid (in the socket, in the seals and in the valve) and the anode, including the coupling elements connected therewith. The grid leads to the socket, i. e., outside of the valve, may also cause adverse couplings, as for reasons associated with the manufacture it is not possible to sufliciently screen off the multi-stage valve towards the outside in the vicinity of the press.

These detrimental couplings are avoided in accordance with the invention by thc fact that it is not the anode of the second system, as mentioned above, but the control grid of the'first system, which is conducted out of the Valve at a point as remote as possible from the remaining lead points. In the case of one single .lead point it is readily possible from a manufacturing standpoint, for example by spraying the bulb with metal, to diminish the couplings of the external lead on metallic portions situated within the valve down to a negligent degree. By leading out the grid separately a reduction of the reaction in the first vsystem `down to one-tenth was obtained by the separate leading-out of the grid as compared with the rst arrangement referred to (separate leading-out of the anode).

As regards the detrimental capacity between the anode of the second system and the control grid of the rst system, it is naturally unimportant which of the two electrodes is screened oi against the remaining electrodes. By the simultaneous leading-out of the second anode in the socket together with the remaining -leads there is caused merely a slight increase in the capacity between the two anodes, which, however, in actual operation, has been found to have no adverse effect on the stability of the amplifier owing to the small values in respect of the anode 40 resistance of the iirst stage and the grid leakage resistance of the second stage.

The valve according to the invention is illustrated in the drawing in a possible form of embodiment wherein Fig. l shows the valve in elevation and Figs. 2 and 3 are diagrammatic representations of the two stages. Within a glass bulb I there are two amplifier stages 2 and 3, which are screened off against each other by means of a close-mesh metal netting 4. Each of these stages in the form of embodiment shown comprises a cathode, a control grid and a screening grid, and an anode. The anode 5 of the rst stage 2 is connected through the lmedium of a condenser 6 with the control grid 1 'of the second stage 3. 8 is the anode resistance of the rst stage, and 9 the grid leakage resistance of the second stage. The screening gridffl of the first stage surrounds the entire cathode and control grid structure thereof in such fashion that the control-grid is shielded against all of the remaining vparts-of the total arrangement. The current supply to the control grid is performed in specially protected fashion by means of a small metal tube I2 at the upper end of the glass bulb I, whilst the remaining conductances are passed through the foot I3. I4 is the cathode, I5 the screening grid, and I6 the anode of the second stage.

I claim:

l. A two-stage high frequency amplifying tube containing two complete thermionic amplifiers coupled together, a metallic screen separating said stages, resistances and a condenser coupling said amplifiers, said resistances and condenser disposed only `on the first stage side of said screen.

2. A `two-stage highv frequency amplifying tube containing two complete thermionic amplifiers coupled together, a metallic screen separating said stages, resistances and a condenser coupling said amplifiers, said resistances and condenser disposed only on the first stage side. of said screen, said tube having the wall `thereof coated with a conductivecoating.adapted to be grounded.

PAUL 

